A Boost-Buck Circuit Anti-Interference Control Method Based on a Disturbance Observer

Abstract

The present invention relates to the technology of power electronic converters, and particularly to an anti-interference control method for a buck-boost circuit based on a disturbance observer. This method adds a control strategy combining a disturbance observer and a PI controller on the basis of a double closed-loop to adjust the output voltage of the Buck-Boost converter so as to eliminate the disturbances of matching or mismatching circuit parameters. In the case of load mutation and input voltage mutation, voltage-current double closed-loop control is adopted, and two disturbance observers are designed to respectively and real-time estimate the uncertain factors in the output voltage and inductor current, and feed forward to the forward channel for compensation to eliminate the disturbances, thereby improving the dynamic characteristics of the system. In the cases of system perturbation, parameter uncertainty and load mutation, this control method can achieve good control over the Buck-Boost converter and improve its response speed and robustness.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and particularly relates to an anti-interference control method for a buck-boost circuit based on a disturbance observer. Background Art

[0002] Wireless Power Transfer (WPT) technology has a wide range of application fields due to its advantages such as reliability, safety, and flexibility. Based on the principle of electromagnetic induction, this technology realizes the non-physical contact power transfer from a power supply device to a power-consuming device. Compared with the traditional contact power supply method, it avoids disadvantages such as poor contact, leakage danger, and poor environmental adaptability, and is not limited by the external harsh environment. It is widely used in some special scenarios, such as electric vehicles, underwater power supply, rail transit, etc. In most cases, it is required that the WPT system maintains a constant voltage output. The general control method is to use a control based on a DC-DC converter on the secondary side. The control performance of the DC-DC converter has a direct impact on the stability of the WPT system.

[0003] The Buck-Boost converter has been widely used in wireless power transfer technology due to its wide voltage conversion range and the ability to increase or decrease the output voltage. The main control objective of the Buck-Boost converter is to control the system to maintain a stable output voltage, and the output voltage is regulated by controlling the on and off of the power switch tube. Since the application scenarios of the WPT system are relatively complex, the system parameters are easily affected by the environment in actual applications. For example, coil offset, load mutation, and input voltage change will all cause the output voltage to deviate from the set value. Traditional control methods are difficult to obtain a system output that meets the actual requirements, often causing the closed-loop control system to be sluggish and generating side effects such as oscillations. In some dynamic wireless charging scenarios, it is required that the system quickly reaches the rated power. Therefore, it is necessary to study a more effective control method for the Buck-Boost converter to enable the system to quickly enter the steady state and quickly recover the steady state under unknown external disturbances, thereby optimizing the dynamic performance of the system. Summary of the Invention

[0004] Aiming at the problems existing in the background art, the present invention provides an anti-interference control method for a Buck-Boost converter based on a disturbance observer.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: An anti-interference control method for a buck-boost circuit based on a disturbance observer. The circuit includes a Buck-Boost converter main circuit and a control circuit; the Buck-Boost main circuit includes an input voltage, a switch tube V g, a freewheeling diode D, an inductor, a capacitor and a resistor; the control circuit includes a current-loop PI controller, a voltage-loop PI controller, a first disturbance observer and a second disturbance observer; the output of the control circuit is connected to the gate of the switching transistor V g , the positive pole of the input voltage is connected to the drain of the switching transistor V g , the source of the switching transistor V g is connected to one end of the inductor and the negative pole of the freewheeling diode D, the positive pole of the freewheeling diode D is connected to one end of the capacitor and one end of the resistor, and the other end of the capacitor, the other end of the resistor and the other end of the inductor are connected to the negative pole of the input voltage; the control method based on this circuit includes: the voltage output value and the inductor current value are used as the two input signals of the disturbance observer in the voltage outer-loop channel, and the system disturbance estimated by the first disturbance observer is fed forward to the voltage-loop PI controller to obtain the ideal value of the inductor current; the voltage output value, the inductor current value and the output value of the current-loop PI controller are used as the three input signals of the disturbance observer in the current inner-loop channel, and the system disturbance estimated by the second disturbance observer is fed forward to the current-loop PI controller to obtain the control quantity, which is sent to the modulation module to obtain the driving signal of the switching transistor, so as to control the stable output of the system.

[0006] In the above buck-boost circuit anti-interference control method based on the disturbance observer, the specific steps of the control method are as follows:

[0007] Step 1. Establish the circuit model of the Buck-Boost converter in the continuous conduction mode of the inductor current;

[0008] Step 1.1. The circuit model when the switching transistor of the Buck-Boost converter is on is:

[0009]

[0010] where, v C is the voltage across the capacitor, i L is the inductor current, V in is the input voltage, C is the capacitance value, L is the inductance value, and R is the resistance value;

[0011] Step 1.2. The circuit model when the switching transistor of the Buck-Boost converter is off is:

[0012]

[0013] Step 1.3. The average switching model is:

[0014]

[0015] where, μ is the switching function, and the expression is:

[0016]

[0017] where \(t\) 0 is the initial time, \(T\) on is the conduction time, and \(T\) is the switching period;

[0018] Step 2: Establish the dynamic model of the Buck - Boost circuit:

[0019]

[0020] where \(d\) 1 and \(d\) 2 are the disturbances caused by the uncertainties in the output voltage and inductor current respectively, and the expressions are:

[0021]

[0022] where \(\mu^*\), \(R\) 0 , \(C\) 0 , \(L\) 0 and \(V\) in0 are the nominal values of \(\mu\), \(R\), \(C\), \(L\) and \(V\) in respectively;

[0023] Step 3: Establish the disturbance observer equation:

[0024]

[0025]

[0026] where and are the estimated values of the disturbances \(d\) 1 and \(d\) 2 respectively, \(z\) 1 and \(z\) 2 are the estimated values of \(v\) C and \(i\) L respectively, and \(l\) 1 and \(l\) 2 are the observer gains;

[0027] The disturbance estimation error is defined as:

[0028]

[0029] Substituting the disturbance observer equation into the above formula, we get:

[0030]

[0031] After arrangement, the disturbance estimation error is obtained:

[0032]

[0033] Step 4: Calculate the control quantity of the composite controller;

[0034] The output u of the voltage outer loop 1 :

[0035]

[0036] where k p1 and k i1 are the proportional and integral coefficients of the voltage outer loop PI controller respectively;

[0037] The output u of the current inner loop 2 :

[0038]

[0039] where k p2 and k i2 are the proportional and integral coefficients of the current inner loop PI controller respectively.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: Since the inductor current is prone to getting out of control under single-loop control, the present invention proposes an anti-interference control method for a Buck-Boost converter based on a disturbance observer, adding a control strategy combining a disturbance observer and a PI controller on the basis of a double closed-loop to adjust the output voltage of the Buck-Boost converter so as to eliminate the disturbances of matching or mismatching circuit parameters. Under the conditions of load mutation and input voltage mutation, a voltage-current double closed-loop control is adopted, and two disturbance observers are designed to respectively and real-time estimate the uncertain factors in the output voltage and the inductor current and feed them forward to the forward channel for compensation to eliminate the disturbances, thereby improving the dynamic characteristics of the system. Under the conditions of system perturbation, parameter uncertainty and load mutation, this control method can control the Buck-Boost converter well and improve its response speed and robustness. Description of the Drawings

[0041] Figure 1 is the circuit diagram of the Buck-Boost converter according to an embodiment of the present invention;

[0042] Figure 2 is the equivalent circuit diagram when the switching tube of the Buck-Boost converter according to an embodiment of the present invention is turned on;

[0043] Figure 3 is the equivalent circuit diagram when the switching tube of the Buck-Boost converter according to an embodiment of the present invention is turned off;

[0044] Figure 4 is the circuit control structure diagram of the Buck-Boost converter according to an embodiment of the present invention;

[0045] Figure 5 The figure showing the comparison result of the output voltage when the system has a load mutation in an embodiment of the present invention;

[0046] Figure 6 is Figure 5 the partial enlarged view when there is a load mutation in

[0047] Figure 7 The figure showing the comparison result of the output voltage when the input voltage of the system mutates in an embodiment of the present invention;

[0048] Figure 8 is Figure 7 the partial enlarged view when the input voltage mutates in Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0051] Next, the present invention will be further described in conjunction with specific embodiments, but it is not a limitation of the present invention.

[0052] This embodiment considers the impacts caused by load mutations and input voltage mutations. For a Buck - Boost converter, a method for anti - interference control using a Disturbance Observer - based (DOB) is proposed, including establishing a mathematical model of the Buck - Boost converter; considering the disturbances in the Buck - Boost circuit and establishing a dynamic model of the circuit; designing two disturbance observers according to the circuit dynamic model to respectively and real - time estimate the uncertain factors in the output voltage and inductor current; feeding the estimated values of the disturbance observers forward to the controller and compensating to eliminate the disturbances, so that the Buck - Boost converter has stronger robustness. In the case of unknown disturbances and uncertain factors, this control method can well control the Buck - Boost converter and improve its response speed.

[0053] This embodiment is implemented through the following technical solutions. As Figure 1 shown, based on the control structure diagram of the anti - interference system for the Buck - Boost circuit, V ref is the output voltage set value, e v is the voltage error, e iis the inductor current error, k d1 is the compensation gain of DOB1, k d1 is the compensation gain of DOB2. The output of the control circuit is connected to the gate of the switching transistor V g ; the positive electrode of V in is connected to the drain of the switching transistor V g ; the source of the switching transistor V g is connected to the inductor L and the negative electrode of the freewheeling diode D. The positive electrode of the freewheeling diode D is connected to the capacitor C and the resistor R. The other end of the capacitor C, the other end of the resistor R, and the other end of the inductor L are connected to the negative electrode of V in . The voltage output value and the inductor current value are used as the two input signals of the disturbance observer in the voltage outer loop channel. The system disturbance estimated by this disturbance observer is fed forward to the voltage loop PI controller to obtain the ideal inductor current value; the voltage output value, the inductor current value, and the output value of the current loop PI controller are used as the three input signals of the disturbance observer in the current inner loop channel. The system disturbance estimated by this disturbance observer is fed forward to the PI controller to obtain the final control quantity, which is sent to the modulation module to obtain the driving signal of the switching transistor, so as to control the stable output of the system.

[0054] A buck-boost circuit anti-interference control method based on a disturbance observer includes a Buck-Boost converter main circuit and a control circuit. The Buck-Boost main circuit is as Figure 2 shown, including the input voltage V in of the Buck-Boost circuit, the switching transistor V g , the freewheeling diode D, the inductor L, the capacitor C, and the resistor R. The control circuit includes a double-loop PI controller and two disturbance observers. The specific steps are as follows:

[0055] S1. Study the Buck-Boost converter circuit in the continuous conduction mode of current, and use the state space averaging method to model the circuit. Figure 2 The following figure shows the equivalent circuit diagram when the switching transistor of the Buck-Boost converter is on. At this time, the circuit model is:

[0056]

[0057] where i L is the inductor current, v C is the capacitor voltage, V in is the input voltage, C is the capacitor value, L is the inductor value, and R is the resistor value;

[0058] Figure 3 The following figure shows the equivalent circuit diagram when the switching transistor of the Buck-Boost converter is off. At this time, the circuit model is:

[0059]

[0060] The average switching model is obtained as follows:

[0061]

[0062] Among them, μ is the switching function, and the expression is:

[0063]

[0064] In the formula, t 0 is the initial time, T on is the conduction time, and T is the switching period.

[0065] S2. Considering the disturbance of the load resistance in the Buck - Boost circuit, the dynamic model of the circuit can be expressed as:

[0066]

[0067] Among them, d 1 and d 2 are the disturbances caused by uncertain factors in the output voltage and inductor current respectively, and the expressions are: μ*, R 0 C 0 L 0 and V in0 are the nominal values of μ, R, C, L, and V in respectively.

[0068] S3. Design a disturbance observer from the system model to estimate the disturbance in the system. The forms of the disturbance observer are:

[0069]

[0070]

[0071] Among them and are the estimated values of d 1 and d 2 respectively, z 1 and z 2 are the estimated values of v C and i L respectively, and l 1 and l 2 are the observer gains.

[0072] The disturbance estimation error is defined as:

[0073]

[0074] Substituting the disturbance observer equation into the above equation, we get:

[0075]

[0076] After arrangement, the disturbance estimation error is obtained:

[0077]

[0078] Proving that the error system is asymptotically stable indicates that the disturbance observer can asymptotically track the disturbance. By reasonably designing the disturbance compensation gains \(l\) 1 and \(l\) 2 , it can be ensured that the output channel is not affected by the disturbance at steady state.

[0079] S4. Design of the composite controller: Feed forward the disturbance estimation value of the disturbance observer to the current-loop PI controller to obtain the final control quantity.

[0080] The output \(u\) 1 of the voltage outer loop and the output \(u\) 2 of the current inner loop are respectively:

[0081]

[0082]

[0083] where \(k\) p1 and \(k\) i1 are respectively the proportional and integral coefficients of the voltage-loop PI controller, and \(k\) p2 and \(k\) i2 are respectively the proportional and integral coefficients of the current-inner-loop PI controller.

[0084] To verify the effectiveness of this control strategy, in this embodiment, a Buck - Boost circuit model is built in Matlab / Simulink, and the double - closed - loop DOB composite control method is applied to control the output voltage of the Buck - Boost circuit, and the disturbances in the output voltage and inductor current are estimated in real time and compensated. Moreover, the control effects of the double - closed - loop DOB control method on the system output are respectively compared with those of the open - loop, single - closed - loop PI, and double - closed - loop PI control methods under the conditions of load mutation and input voltage mutation.

[0085] The DOB parameters are taken as \(k\) 1 = 0.0001, \(k\) 2 = - 0.475, \(l\) 1 = \(l\) 2 = 10000. The proportional coefficient and integral coefficient of the voltage outer loop of the PI controller \(k\) p1 = 3, \(k\) i1 = 10, and the proportional coefficient and integral coefficient of the current inner loop of the PI controller \(k\) p2 = 0.005, \(k\)i2 The simulation experiment research is carried out with =1. The parameters of the Buck - Boost converter are shown in Table 1.

[0086] Table 1 Design parameters of the Buck - Boost converter

[0087]

[0088] To verify the ability of the double - closed - loop DOB to suppress unknown load changes, the simulation time is 1 s. At 0.5 s, the load resistance changes from the nominal value R 0 =50Ω to R = 100Ω. The simulation experiment response curves of the output voltage under the conditions of open - loop, single - closed - loop PI, double - closed - loop PI control, and double - closed - loop DOB composite control when the load resistance increases are as Figure 5 shown, Figure 6 and the local enlarged view is shown as follows.

[0089] To verify the ability of the double - closed - loop DOB to suppress unknown input voltage changes. The simulation time is 1 s. At 0.5 s, the input voltage changes from the nominal value V in0 =60V to V in =80V. The simulation experiment response curves of the output voltage under the conditions of open - loop, single - closed - loop PI, double - closed - loop PI control, and double - closed - loop DOB composite control when the input voltage increases are as Figure 7 shown, Figure 8 and the local enlarged view is shown as follows.

[0090] From Figures 5 - 8 it can be seen that the open - loop cannot eliminate the offset caused by sudden changes in load resistance and unknown input voltage. The single - closed - loop PI control and double - closed - loop PI control can effectively eliminate the influence of unknown disturbances and uncertain factors, but their recovery performance under load mutations and uncertain factors is limited, the settling time is long, and the output voltage deviation is large. The double - closed - loop DOB composite control method described in this embodiment can effectively compensate for the influence of sudden changes in load resistance and input voltage, and has better disturbance suppression ability and control performance compared with the double - closed - loop PI controller.

[0091] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all equivalent replacements and obvious changes made by using the content of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A buck-boost circuit anti-interference control method based on a disturbance observer. The circuit includes a Buck-Boost converter main circuit and a control circuit; the Buck-Boost main circuit includes an input voltage, a switching transistor (V g ), a freewheeling diode (D), an inductor, a capacitor, and a resistor; the control circuit includes a current-loop PI controller, a voltage-loop PI controller, a first disturbance observer, and a second disturbance observer; the output of the control circuit is connected to the gate of the switching transistor (V g ), the positive pole of the input voltage is connected to the drain of the switching transistor (V g ), the source of the switching transistor (V g ) is connected to one end of the inductor and the negative pole of the freewheeling diode (D), the positive pole of the freewheeling diode (D) is connected to one end of the capacitor and one end of the resistor, and the other end of the capacitor, the other end of the resistor, and the other end of the inductor are connected to the negative pole of the input voltage; It is characterized in that: The control method based on this circuit includes: the voltage output value and the inductor current value are used as the two input signals of the disturbance observer in the voltage outer loop channel, and the system disturbance estimated by the first disturbance observer is fed forward to the voltage loop PI controller to obtain the ideal value of the inductor current; the voltage output value, the inductor current value, and the output value of the current loop PI controller are used as the three input signals of the disturbance observer in the current inner loop channel, and the system disturbance estimated by the second disturbance observer is fed forward to the current loop PI controller to obtain the control quantity, which is sent to the modulation module to obtain the drive signal of the switching tube, thereby controlling the stable output of the system.

2. The buck-boost circuit anti-interference control method based on a disturbance observer according to claim 1, It is characterized in that: The specific steps of the control method are as follows: Step 1: Establish a circuit model of a Buck-Boost converter in the continuous conduction mode of inductor current; Step 1.1: The circuit model when the switch of the Buck-Boost converter is on is: where v C is the voltage across the capacitor, i L is the inductor current, V in is the input voltage, C is the capacitance value, L is the inductance value, and R is the resistance value; Step 1.2: The circuit model when the switch of the Buck-Boost converter is off is: Step 1.3: The average switch model is: where μ is the switching function, and the expression is: where t 0 is the initial time, T on is the conduction time, and T is the switching period; Step 2: Establish a dynamic model of the Buck-Boost circuit: where d 1 and d 2 are the disturbances caused by uncertainties in the output voltage and inductor current respectively, and the expressions are: Among them, μ*, R 0 , C 0 , L 0 and V in0 are the nominal values of μ, R, C, L, and V in respectively; Step 3: Establish a disturbance observer equation: Wherein, and are the disturbance estimation values of d 1 and d 2 respectively, z 1 and z 2 are the estimated values of v C and i L respectively, and l 1 and l 2 are the observer gains; Disturbance estimation error is defined as: Substituting the disturbance observer equation into the above formula, we get: After arrangement, the disturbance estimation error is obtained: Step 4: Calculate the control quantity of the composite controller; Output u of the voltage outer loop 1 : where k p1 and k i1 are the proportional and integral coefficients of the voltage outer-loop PI controller, respectively; Output u of the inner current loop 2 : where k p2 and k i2 are the proportional and integral coefficients of the current inner-loop PI controller, respectively.

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